Constant pressure regulation of grader blades

ABSTRACT

By providing the work blade of a grader with a hydraulic regulation system where pressure limiting valves (14, 15, 16, 17) guide pressure reducing valves (10, 11, 12, 13) a constant pressure regulation of the work blade is achieved so that the work pressure set by the operator from his cab is maintained almost independent of the irregularities of the underlying surface.

TECHNICAL FIELD

The present invention relates at first to a device for constant pressureregulation of grader blades for the preparation of roadways. Theinvention has at first been developed for graders but can also e.g. beused for snow-ploughs and other devices doing road surface work or othersurface work.

Consequently, the invention relates to the hydraulic system used toregulate grader blades and excavator blades on graders and other workmachines used both for snow removing purposes and for construction work(compare the Swedish patent application 8402517-0).

The terminology used for workblades in relation to work machines arethat the term "excavator blade" is used for processing and transport ofmasses and that the term "grader blade" is used as a definition of theworkblade normally arranged under a grader and between its front andrear pair of wheels. The term "workblade" therefore comprises these twotypes of blades. Hereafter in the description the term "grader blade" isused as a definition of the workblade but naturally other types ofworkblades are included. Furthermore the term "cutting edge" is used forthe outmost edge of a workblade.

BACKGROUND ART

The method of placing a road-grader blade against the roadway has almostbeen unchanged since road-grader blades for the first time were takeninto use many centuries ago. The force used to press the cutting edgeagainst the roadway has always been estimated by the operator withoutany special means of assistance. Consequently, the applied force differsa lot in magnitude in each specific case and was fully dependent of theactual operator's experience and skill. Consequently, the work carriedout has been more dependent of the operator's experience and skill thanof the hardness and the geometric profile of the foundation. Road workcarried out has therefore varied a lot in quality. When the road-graderblade has been pressed towards the roadway with a force not big enoughthe result of the work carried out was of bad quality. When theroad-grader blade has been pressed towards the roadway with a force toobig, damages in the roadway have occured and also resulted in too quickwear of the cutting edge which caused enormous costs in changes.

THE PURPOSE OF THE INVENTION

The purpose with the present invention is to produce a method and ameans possible provide constant pressure regulation of a road-graderblade so that the cutting edge is always pressed towards the roadwaywith optimum force related to each job opportunity independent of theoperator's experience and skill. The device makes it possible tomaintain a constant contact pressure between the cutting edge and theroadway also at variations in the hardness of the roadway, geometricshape and macrostructure. The device also maintains constant pressurewhen the road-grader blade is tilted or turned round its vertical axisand also in vertical curves.

Accordingly, the purpose of the invention is for example not to cut offthe road surfaces or to damage pavements. Furthermore, the presentinvention provides a possibility to a larger extent than previous topredict when to exchange the cutting edge of a grader and so that theresources held by the stock of graders can be further optimized. Theinvention taken into practise by the hydraulic system described asfollows, consequently gives constant contact force towards the roadwayindependent of the shape of the roadway. The contact force in theembodiment described is electrically operated from the drivers cabseparately for each cylinder (first and second).

A further purpose with the invention is to solve the problems related tothe difficulties that arose in the winter when a grader is going to cutthe roadways and the pavements clean from snow and ice. It is then verydifficult for the operator to adapt the vertical force of theroad-grader blade, in other words the pressure of the road-grader bladetowards the roadway so that the roadway and e.g. adjacent pavements arenot scraped. Such damage causes great economic losses every year and isalso very difficult to avoid. Furthermore, as previously mentioned anextremely high wear of the cutting edge of the grader blade is achievedwhich causes shorter intervals for exchange of the cutting edges aswould be necessary if the wear of the cutting edges only was caused bynormal use.

SUMMARY OF THE INVENTION

By forming the grader blade hydraulic circuit of a work machine in twoseparately and individually adjustable hydraulic circuits eachseparately operating the vertical force of the left and the right sideof the grader blade towards the roadbed, an extended possibility toregulate the grader blade of the work machine is achieved. Together withthis two-part separated hydraulic circuit the hydraulic circuits alsocontain the possibility for the operator to chose the ground pressuresuitable under the present conditions. The operator has also thepossibility in using "quick-driving" of the grader blade, meaning amomentary lowering of the grader blade. The operator can also from thedrivers cab switch between constant pressure regulation of the graderblade and manual driving of the grader blade, meaning operation with aconventional hand lever operated valve.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described by working examples withnumerals related to the enclosed drawings where,

FIG. 1 shows a partly schematic hydraulic circuit according to theinvention where the hydraulic circuits are shown as blocks

FIG. 2 shows the hydraulic circuit in the block A in FIG. 1

DESCRIPTION OF THE INVENTION

Below, one mode of the invention applied to a grader will be described.Numerals in consecutive order to the figures makes it easier tounderstand the invention.

The grader blade on a road-grader is normally suspended between thefront pair of wheels and the rear pair of wheels, that is centrallyunder the grader, in a table which can be operated from the drivers cabof the grader. The table can in this respect be turned so that the angleof the grader blade in relation to the driving-direction is changed. Onehydraulic cylinder for vertical operation of the grader blade is mountedon each side of the grader. These hydraulic cylinders, hereafter calledthe first and the second hydraulic cylinder C1 and C2, are also operatedby the operator from the drivers cab of the grader. With help from thesecylinders the operator can e.g. choose the vertical force of the graderblade towards the roadbed whereby the roadbed establishes the verticalposition of the grader blade.

The hydraulic circuit in the block A in FIG. 1 is arranged with threebottom gates indicated P, T and Dr. The P-gate is connected to a pump 1arranged to pressurize the hydraulic circuit A. The T-gate is connectedto a tank for containing hydraulic fluid when the circuit A is beingdrained. The Dr-gate is used when draining the block of hydraulic fluid.One purpose of such a division of T-gate and Dr-gate is to avoidpressure variations which could affect the function of the circuit.Furthermore, the block A is provided with left plus-and minus gates A1,B1 for the left hydraulic cylinder C1 and right plus-and minus gates A2,B2 for the right hydraulic cylinder C2. Also, FIG. 1 shows the relationof the block A according to the rest of the blocks in the system forconstant pressure regulation of the grader blade.

A block B is drawn in FIG. 1 to show a solution of the system ofregulation if a pump which is not pressure compensated is used. Thisblock is eliminated if a pressure compensated pump is used and the blockB is then replaced by a T-coupling with connections from the pump beingpressure compensated to the P-gate at the block A and to a hand levervalve of conventional type. The valve V in direct connection to the pump1 is drawn as a suggestion to arrange a choice possibility between theconventional hand lever valve, the block C, and the constant pressureregulation, block A. The valve V is hereby drawn as a manually operatedvalve, operated by the operator from the driver's cab of the grader.Depending on the choice of a hand lever valve the valve V is chosen. Ifa pressure compensated pump is used and the block B is replaced by aT-coupling another type of hand lever valve is preferably chosen so thatthe valve V can be excluded. Further, the block B is arranged with anexpansion tank E in order to eliminate hydraulic fluid via a drain valveif the pressure increases beyond the allowed level. This expansion tankis also eliminated if a pressure compensated pump is used.

Further, a block C is drawn into FIG. 1 in order to indicate the normalfunction of the hand lever valve in formerly used regulation systems forgraders. This block is not shown in detail in the present inventionsince the hand lever valve is of conventional type and therefore is ofordinary shape and function.

Also, there are two blocks D indicating back pressure valves arranged ateach cylinder (C1, C2) in order to prevent leakage from the minus-sidesof the cylinders (C1, C2) to the tank. This is a nominal arrangementtogether with hand lever valves of the slide type to prevent the graderblade falling.

The P- and the T-gates are, see FIG. 2, inside the block A connected toat least one 4-way electric directional valve which in its normalposition keeps the hydraulic circuit drained from hydraulic fluid viathe B-gate of the valve. The directional valve opens the hydrauliccircuit so that hydraulic fluid from the pump can reach the circuit whenthe magnet of the valve is being influenced. In the mode of exampleshown in FIG. 2 a first 4-way electric directional valve 2 is providedfor the first part of the block and a second 4-way electric directionalvalve 3 is provided for the other part of the block to pressurize anddepressurize the parts of the hydraulic circuit A.

The hydraulic circuit A in the block is then equipped with a leftplus-gate A1 and a left minus-gate B1 for the plus- and the minus-sideof the left hydraulic cylinder C1. The plus-side is defined as the sideof the cylinder which makes the piston-rod protrude when pressurized andthe minus-side is defined as the side of the cylinder which makes thepiston-rod retract into the cylinder when pressurized. Correspondinggates are arranged at the right hydraulic cylinder, that is one rightplus-gate A2 and one right minus-gate B2.

These four cylinder gates A1, B1, A2 and B2 in the block are eachconnected to a pilot operated back valve so that the left plus-gate A1is connected to a first back valve 6, the right plus-gate A2 isconnected to a second back valve 7, the left-minus gate B1 is connectedto a third back valve 8 and the right minus-gate B2 is connected to afourth back valve 9. All back valves are, as previously mentioned, pilotoperated so that they open at a specific input pressure in the hydrauliccircuit A.

Each of these back valves 6, 7, 8, 9 are connected to the directionalvalves 2, 3 via the REG-gate on each of four 3-way pressure reducingvalves so that the first back valve 6 is connected to a first pressurereducing valve 10, the second back valve 7 is connected to a secondpressure reducing valve 11, the third back valve 8 is connected to athird pressure reducing valve 12 and the fourth back valve 9 isconnected to a fourth pressure reducing valve 13. Then each pressurereducing valve 10, 11, 12 and 13 is provided with a drain-gate R to thetank. Each pressure reducing valve is pressure controlled so that thestream of fluid is accepted to a predetermined level of pressure in onedirection and if the level is exceeded the stream of fluid changesdirection and will be drained by the R-gates of the valves. Further,each pressure reducing valve 10, 11, 12 and 13 is connected each one toa pressure limiting valve so that the first pressure reducing valve 10is operated by a first proportional pressure limiting valve 14 so that apredetermined pressure set by this valve 14 maintains the pressure atthe REG-gate of the pressure reducing valve 10. Further, the secondpressure reducing valve 11 is operated by a second proportional pressurelimiting valve 15 so that in the same way a predetermined pressure setby this valve 15 maintains the pressure at the REG-gate of the pressurereducing valve 11. The third pressure reducing valve 12 is operated by afirst pressure limiting valve 16 and the fourth pressure reducing valve13 is operated by a second pressure limiting valve 17. The purpose ofthe two pressure limiting valves 16, 17 are to calibrate the scales ofthe proportional pressure limiting valves 14 and 15. The calibration iscarried out so that the zero-level on the proportional pressure limitingvalves 14 and 15 correspond to the "float-level" on the grader blade,that is the condition when the blade is slowly moving upwards from theroadway. Besides, each pressure limiting valve 14, 15, 16, 17 isequipped with a draining gate Dr for externally draining, whereby thedraining gates Dr of the first and the second pressure limiting valves16, 17 are connected to an electrically operated 2-way directional valve18 having a magnet 19. The directional valve 18 makes it possible toeliminate the draining of the first and the second pressure limitingvalves 16, 17 so that a fast lowering of the grader blade is achieved.

A first pressure gauge 20 is directly connected to the plus-side of theleft hydraulic cylinder C1 via the connection M_(A1) of the hydrauliccircuit A and a second pressure gauge 21 is directly connected to theplus-side of the right hydraulic cylinder C2 via the connection M_(A2)of the hydraulic circuit A so that the operator directly can read thehydraulic pressure out to the plus-sides of the cylinders. There is alsoa separate third pressure gauge 22 belonging to the system in order tobe connected to the hydraulic circuit A at a number of measuring pointsM_(B1), M_(B2), M_(P1) and M_(P2) arranged as measuring connectors. Atthe connectors M_(B1) and M_(B2) measures of the minus-sides of thehydraulic cylinders C1, C2 are carried out, at the connectors M_(P1) andM_(P2) measures of the input pressure at the left and at the right sideof the hydraulic circuit A are carried out. The measuring connectorM_(P) is used for examining the total input pressure of the circuit A,that is just in front of the two directional valves 2, 3.

The function of the block A, that is the hydraulic circuit A isdescribed below mainly with references to FIG. 2.

The hydraulic circuit A (in this case block A in FIG. 2) is fed withconstant pressure by a hydraulic pump 1 (shown in FIG. 1) in its P-gate(FIG. 2). The pressure is then blocked by a first electrically operated3-way directional valve 2 and a second electrically operated 3-waydirectional valve 3 when the magnets 4, 5 of the directional valves 2, 3are deactivated (the normal position shown in FIG. 2). At the same timethe system is drained and that is when the B-gates of the directionalvalves 2, 3 are connected to a tank via the T-gate (FIG. 2) and the fourpilot operated back valves 6, 7, 8, 9 are closed. Accordingly thehydraulic circuit A is deactivated and "normal" driving of the graderblade via the hand lever valve (shown only in block C in FIG. 1) ispossible.

Activation of the hydraulic circuit A is carried out when a voltageactivates the magnets 4, 5 of the directional valves 2, 3 so that thepressure can enter the two separate hydraulic circuits. The block A inFIG. 2 is divided into one separate hydraulic circuit for each hydrauliccylinder C1 and C2.

Feeding pressure has therefore reached the front of the P-gates of thefour 3-way pressure reducing valves. Pilot pressure (=input pressure)opens simultaneously the four pilot operated back valves 6, 7, 8, 9. Thepressure out to the gates of the hydraulic cylinders C1, C2 via theREG-gates of the pressure reducing valves 10, 11, 12, 13 is establishedby the setting of the four pressure limiting valves 14, 15, 16, 17 whichoperate as pilot valves for the pressure reducing valves 10, 11, 12, 13where as previously mentioned the pilot valves 14 and 15 areproportional pressure limiting valves and the pilot valves 16 and 17 areordinary pressure limiting valves.

The adjustment of the floating point of the grader blade is done bysetting the two proportional limiting valves 14 and 15 to a minimumvalue, that is O-position on the two scales connected to the valves, sothat "zero-pressure" reach the plus-sides of the hydraulic cylinders C1,C2. Then the pressure limiting valves 16 and 17 are pressure adjusted toa value so that the grader blade is lifting from the roadbed and slowlymoving upwards, that is the contact force towards the roadway is 0.

The pressure towards the roadway is then selected by the operator fromthe operators cab by the two proportional pressure limiting valves 14and 15. The valves 14, 15 are electrically operated via a potentiometerand a guide card separately for each hydraulic cylinder C1 and C2.

The four 3-way pressure reducing valves 10, 11, 12, 13 operate both aspressure reducing valves and as pressure limiting valves in thehydraulic circuit A. That is, if the level of the set pressure at theREG-gates of the pressure reducing valves 10, 11, 12, 13 has not beenreached, these valves are open (P to REG) and hydraulic fluid is filleduntil set pressure is reached.

If the pressure reaches a higher value than set by the pressure limitingvalves 14, 15, 16, 17 the pressure reducing valves 10, 11, 12, 13 changefunction and open the connections from their REG-gates to their R-gateswhich are connected to to the tank so that the pressure is drained untilset value on the REG-gate of the valves are attained.

Activation of the magnet 19 of the electric directional valve 18 means"quick-driving" (also known as differential-driving, which imply a fastlowering of the grader blade) of the hydraulic cylinders in theplus-direction if at the same time maximum pressure (about 80-100 bar)is given to the proportional pressure limiting, valves 14 and 15.

In order to make the hydraulic cylinders move in the plus-direction thedead weight of the grader blade (about 2000-2500 kg) must effect thehydraulic cylinders C1, C2. In this case the pressure reducing valves 12and 13 at the minus-sides of the hydraulic cylinders C1, C2 are forcedto the open position (P to REG) and the minus-sides of the cylinders areconnected to feeding pressure (=max 160 bar). If at the same time thepressure reducing valves 10 and 11 are being set by the proportionalpressure limiting valves 14 and 15 so that the pressure transmitted tothe plus-sides of the hydraulic cylinders reaches 80-100 bar thehydraulic cylinders move in the plus-direction and a fast lowering ofthe grader blade is achieved.

The invention can within the scope of the following claims be used bydifferent types of work machinery where constant pressure regulation ofthe work blade of the machine is desirable. The invention is thereforenot limited to concern only a road machine or a road grader.

We claim:
 1. A method of regulating pressure on a work blade on a roadmachine so that a hydraulic system with a first hydraulic cylinder (C1)and a second hydraulic cylinder (C2) regulates the vertical force of thework blade towards an underlying surface, characterized by that thehydraulic system regulates the vertical force of the work blade towardsthe underlying surface whereby the setting of the work pressure at thefirst hydraulic cylinder (C1) by a first pressure limiting valve (14)and the setting of the work pressure at the second hydraulic cylinder(C2) by a second pressure limiting valve (15) is maintained when thefirst pressure limiting valve (14) is guiding a first pressure reducingvalve (10) and the second pressure limiting valve (15) is guiding asecond pressure reducing valve (11) at plus-sides of the hydrauliccylinders and that one more pressure limiting valve (16) is guiding athird pressure reducing valve (12) and that one more pressure limitingvalve (17) is guiding a fourth pressure reducing valve (13) in order tobalance the pressure at minus-sides of the hydraulic cylinders (C1,C2).2. Device for constant pressure regulation of a work blade on a roadmachine where a hydraulic system comprising a first hydraulic cylinder(C1) operating on one side of the work blade and a second hydrauliccylinder (C2) operating on the other side of the work blade is arrangedto regulate the vertical force of the work blade towards the underlyingsurface, characterized by that each hydraulic cylinder (C1,C2) is fedwith a constant pressure at a plus-side of each cylinder and a constantpressure at a minus-side of each cylinder and that these pressures, aremaintained by the arrangement of two pressure reducing valves (10,11)operated by two proportionally pressure limiting valves (14,15) on theplus-sides of the hydraulic cylinders and by the arrangement of two morepressure reducing valves (12,13) operated by two more pressure limitingvalves (16,17) in order to balance the pressure on the minus-sides ofthe hydraulic cylinders.
 3. A hydraulic system according to claim 2,characterized by that differential driving is achieved by a directionalvalve (18) mounted in order to stop the draining of the minus-sides ofthe pressure limiting valves (16,17).
 4. Device according to claim 3,characterized by that the constant pressure regulation hydraulic circuit(A) of the work blade is provided as an alternative to an existing handlever valve in a road machine.